PHP UTF16 to UTF8 conversion

Tried to read UTF16 con开发者_StackOverflow中文版tents from CSV and convert it into UTF8 using mb_convert_encoding and do utf8_decode on the text. Now compare this text to the utf8_decoded text from webpage and write output to a xls.This works fine for almost all languages (German, English, French, Espanol, Italiano, Indonesian,....) except (Japanese, Russian, Turkei and few characters in Polski)

Tried iconv also....All in vain. Seek some help handling this UTF16 to UTf8 conversion